Some commercial establishments, such as restaurants, produce a considerable amount of waste or drainage water which often contains high levels of grease or oil. Such contaminants can adversely affect the sewage treatment plants and can clog up the sewers. Therefore, most jurisdictions require that such grease and oil be removed from the wastewater at the commercial establishment before it is permitted to enter the sewage system. To effect such removal, a restaurant will typically provide a grease trap on its wastewater outlet line. Essentially, wastewater passes into the grease trap at one end and within the grease trap, the grease which has a lower specific gravity than water rises and forms a layer on top of the grease trap. A fluid outlet from the grease trap is positioned below the level of the grease layer to permit substantially grease free wastewater to be removed. In this way, the grease is collected in the grease trap and it may be periodically removed by direct bailing the grease out of the top of the grease trap. The grease is then disposed of as solid waste, for example, at landfill sites.
One problem with conventional grease traps is that particles of food are also present in the wastewater stream, such as bits of lettuce, meat and other waste solids. These solid waste particles have two significant effects. First, they significantly increase the volume of the waste layer collected. As a result, the grease trap becomes filled quickly and the collected waste must be removed frequently. Second, the bits of solid matter caught in the grease trap tend to decompose, anaerobically, which creates noxious gases, making the job of manually bailing the grease from the grease trap extremely unpleasant. Thus the prior art devices suffer from being both labour intensive (i.e. they fill quickly and require more frequent cleaning) and extremely unpleasant to maintain.
A number of devices for separating waste from wastewater are already known. U.S. Pat. No. 1,407,936 discloses an apparatus and method for separating matter from effluents. The apparatus includes a container which is wide at its inlet end and narrow at its outlet end. The effluent enters the container through an inlet pipe at the bottom of the container, and the effluent stream is directed upward. At that point, solid particles settle on the floor of the container, and can be removed manually through a separate valve created for that purpose. Meanwhile, the effluent stream continues through the container, and the floating waste separates from the water stream, which is directed to the outlet pipe at the opposite end of the container.
This device separates solid waste from the floating waste, such as grease, and takes the solid waste out of the effluent stream. However, the container must be manually emptied of solid waste separately from the removal of the grease. This is a time-consuming activity, and it must be done fairly frequently to prevent clogging of the inlet pipe.
U.S. Pat. Nos. 2,138,985, 3,849,311 and 4,372,854, for example, also disclose devices for separating light waste, such as oil or grease, from water. However, the devices in these patents all suffer from the problem that solid waste is trapped in the trap.